This project seeks to identify a central factor driving aging in order to develop targeted interventions to delay the onset or even reverse aging-related pathologies. My preliminary data demonstrate caloric restriction (CR), a proven intervention for increasing lifespan stimulates endogenous production of hydrogen sulfide gas and this is necessary for the stress resistance benefits of CR. Here, we test age related decline of endogenous hydrogen sulfide production and if it is delayed by a specific and more clinically favorable form of dietary restriction, methionine restriction, as a means to increase metabolic fitness, stress resistance and longevity.